1. Field
The present invention relates to a synthetic resin tube structure, which is formed by welding two synthetic-resin members together.
2. Description of the Related Art
For a case where a multicylinder engine is used, an intake manifold, in which the same number of intake passages as that of cylinders are formed, is provided between the engine and a throttle body. A plurality of intake pipes, each having a different shape and intake passage, are formed in the intake manifold, and hence an intake manifold made of a synthetic resin has been provided in terms of ease of formation of the shape of the intake pipe, reduction in weight, reduction in cost, and the like, as shown in JP 2005-69118 A.
Here, a basic structure of the intake manifold made of the synthetic resin, which is described in JP 2005-69118 A, is described with reference to FIGS. 5 to 7. An intake manifold 60 includes two synthetic-resin members, i.e., a first synthetic-resin member 62 and a second synthetic-resin member 64 and is formed by welding the two synthetic-resin members 62 and 64 together. The first synthetic-resin member 62 includes: a flange 68 to be connected to an engine 66; and a plurality of first divided pipes 70a, 70b, and 70c integrally formed with the flange 68. A plurality of bores 72a, 72b, and 72c, each serving as a passage to the engine 66, are formed through the flange 68. Each of the first divided pipes 70a, 70b, and 70c has a semicircular or semi-elliptical sectional shape in a direction perpendicular to a longitudinal direction thereof in most parts.
The second synthetic-resin member 64 includes: a plurality of second divided pipes 74a, 74b, and 74c to be welded to the flange 68 and the plurality of first divided pipes 70a, 70b, and 70c; and connectors 76 for connecting the plurality of second divided pipes 74a, 74b, and 74c to each other in a fixed manner. Each of the second divided pipes 74a, 74b, and 74c has a semicircular or semi-elliptical sectional shape in a direction perpendicular to a longitudinal direction thereof in most parts. An edge of each of the second divided pipes 74a, 74b, and 74c on the side of the flange 68 is referred to as a joint edge 78.
First welding ribs 80 are formed on both sides of each of the plurality of first divided pipes 70a, 70b, and 70c. A first fore-end portion 82 is formed on a free fore-end side of each of the first welding ribs 80 provided on both the right and left sides. If a plane which connects the first fore-end portions 82 to each other is indicated by a line P-P in FIG. 6 and a reference plane of the flange 68 on the side of the first divided pipes 70a, 70b, and 70c is indicated by a line Q-Q in FIG. 6, then the line P-P is set to be parallel to the line Q-Q. The reference plane of the flange 68 is perpendicular to a direction in which the bores 72a, 72b, and 72c of the flange 68 extend. Although the reference plane of the flange 68 (at a position of the line Q-Q) is an end surface 83 of the flange 68, which is on the side to be connected to the first divided pipes 70a, 70b, and 70c, in FIG. 6, the reference plane may also be an end surface 84 of the flange 68, which is brought into contact with the engine 66. On the other hand, second welding ribs 85 are formed on both the right and left sides of each of the plurality of second divided pipes 74a, 74b, and 74c, whereas a second fore-end portion 86 is formed on the fore-end side of each of the welding second ribs 85 provided on both the sides.
For welding the first synthetic-resin member 62 and the second synthetic-resin member 64 together, the first welding ribs 80 provided on both the right and left sides of each of the first divided pipes 70a, 70b, and 70c are brought into contact with the second welding ribs 85 provided on both the right and left sides of each of the second divided pipes 74a, 74b, and 74c to bring the first fore-end portions 82 provided on both sides of the fore-end of each of the first divided pipes 70a, 70b, and 70c into contact with the second fore-end portions 86 provided on both sides of the fore-end of each of the second divided pipes 74a, 74b, and 74c, thereby bringing the joint edges 78 of the second divided pipes 74a, 74b, and 74c into contact with the flange 68. In this state, all the portions being in contact with each other are welded by vibration welding. A direction, in which the first divided pipes 70a, 70b, and 70c and the second divided pipes 74a, 74b, and 74c are vibrated, is parallel to the line P-P (line Q-Q), and the welding is performed in a direction perpendicular to the line P-P (in a direction indicated by an arrow of FIG. 5). Along with the welding between the first divided pipes 70a, 70b, and 70c and the second divided pipes 74a, 74b, and 74c, the second divided pipes 74a, 74b, and 74c and the flange 68 are welded to each other. As a result of the welding, a plurality of pipes 88a, 88b, and 88c are formed by the first divided pipes 70a, 70b, and 70c and the second divided pipes 74a, 74b, and 74c (FIG. 5). Inside the pipes 88a, 88b, and 88c, passages 90a, 90b, and 90c, each having a circular or elliptical cross section, are respectively formed.
Ends on the side of the passages 90a, 90b, and 90c are respectively in communication with the bores 72a, 72b, and 72c of the flange 68. At ends on the other side of the passages 90a, 90b, and 90c, ports 92a, 92b, and 92c are respectively formed. Here, if the respective center positions of the ports 92a, 92b, and 92c are center points 94a, 94b, and 94c, then a plane containing the center points 94a, 94b, and 94c are positioned on the line P-P.
The direction, in which the vibrations for welding are made, is set to be parallel to the line Q-Q of the reference plane of the flange 68, and hence a position of the plane which connects the respective center points 94a, 94b, and 94c of the ports 92a, 92b, and 92c also becomes parallel to the line Q-Q. A total width (length A) of the three pipes 88a, 88b, and 88c at the positions where the ports 92a, 92b, and 92c are situated is equal to a width (length A) of portions of the pipes 88a, 88b, and 88c, which are connected to the flange 68. In other words, a large space is required for the pipes 88a, 88b, and 88c at the positions where the ports 92a, 92b, and 92c are situated.